Pipe element, especially for exhaust pipes in motor vehicles, and method for producing the same

ABSTRACT

The invention relates to a method for producing a pipe element ( 1 ) for pipes that are subject to vibrating stress, especially for exhaust pipes in motor vehicles. Said pipe element consists of a preprofiled strip ( 2; 3 ), especially a metal strip, that is wound in convolutions with bellow-shaped windings ( 4; 22 ). The wound layers produced by a strip width are interlinked in a single-hooked or multi-layer clasp-type bond ( 9; 19 ) by positive locking, welding or similar joining methods. The Strip ( 2; 3 ) is preprofiled with at least one stitch that is off-set from the plane by deflection into a kind of circuit with web heights (h 1,  h 2 ) of the bellows ( 4; 22 ) that are multiples of the strip thickness.

The invention relates to a method of making a conduit forvibration-stressed conduit systems, in particular as a motor-vehicleexhaust pipe, from a preshaped strip, in particular a metal strip, thatis helically wound with bellows-like folds, the wound-together layersformed by a strip width having singly hooked-together or multilayerinterlocked edges joined by interfitting, welding, or a similar joiningprocess and to a conduit produced according to the method.

The goal of such conduits, that are wound as spiral-shaped woundinterlocked tubes or spiral-shaped interhooked tubes, that typicallyleak a little in use, is to connect vibrating pipes to each other so asto decouple them with respect to vibration. An element of such a conduitis in many cases a metall bellows. Since the large difference indiameters in the folds of the bellows create turbulence, as a rule ametal hose is integrated into the conduit so as to ensure laminarexhaust-gas flow. To this end attention must be paid that during the usethere is no noise generated by engagement of the metal hose inside thebellows. In order to achieve this and gas tightness, in many case a wiremesh surrounds the hose. German 198 20 863 describes a flexible conduitwherein alternatively to a wire mesh the metal hose and the metalbellows are fixed together at specific locations.

The known embodiments require different manufacturing processes for theindividual elements as well as expensive s positioning and assemblyoperations. Since, in addition to the manufacturing of the individualparts of the described conduits the assembly process is expensive, ithas been proposed for economic reasons to manufacture the metal bellowsand the internal hose in a single manufacturing process by helicalwinding. Such a manufacture so-called exhaust hose is known from German38 09 210. The there described helical winding of a preshaped metalstrip has however two disadvantages. On the one hand the conduits is notcompletely gas tight. On the other hand the geometric shape of thebellows-like corrugations produced on manufacture of the bellow and hosefrom a preshaped metal band is subject to substantial limitations, sothat it is not possible in many cases to attain the desired static anddynamic stiffness required. This problem is caused by the considerableaxial and radial deformation of the hose and bellows parts relative toeach other, since during winding the different dimensions of a preshapedmetal strip are limited strongly by the production limits of forming thebellows folds with the desired geometric relationships.

German utility model 76 31 806 discloses a corrugated hose formed in oneor more layers by helically winding a profiled strip or interfittedpreshaped tubular sections of metal or plastic with gas-tight strip ortube edges joined together by interfitting, welding, gluing, or thelike. For the best possible laminar gas flow the inner strip or tubeedge is unitarily connected with an axially extending tubular extensionthat inwardly covers at least the adjacent bumpy helical or annularspace.

It is an object of the invention to provide a method and a conduit ofthe above-described type whereby a one-step manufacturing processwithout subsequent assembly produces a geometrically so constructedconduit that a simple vibration-responsive product is achieved with thenecessary static and dynamic stiffness.

This object is achieved according to the invention with a method whereinthe strip is preshaped into an arcuate shape with webs heights of thebellows-shaped folds that are a multiple of a strip thickness. As manytests have confirmed, by not using the conventional planar-pathroller-shaping method and instead using at least one roll stand outsidethe plane by arrangement of roller pairs on a spiral-shaped path whosecurvature increases up to nearly the curvature of the conduit, it ispossible to preshape the strip with transversely projecting webs thatare 25 to 75 times bigger than the strip thickness. With a standard webthickness of 0.2 mm or 0.3 mm the web height can be 5 mm to 7.5 mm or 15mm to 22.5 mm. According to preferred suggestions of the invention, theradially inwardly and preferably radially outwardly projecting webs witha fold height much greater than the known systems produce a conduit ofgreat flexibility and elasticity. A spiral shape, produced by rollingoutside a plane, in the final shape is advantageous from a shaping pointof view because it increases the ability to flex without materialfailure so that large variations in shape and bellows-like turns orfolds of different geometry or configuration can be produced. The turnsor bellows folds are not point symmetrical but wave like, with a helicalshape symmetrical to an axis.

According to an embodiment of the invention, one strip edge of onewinding layer covers a valley of an adjacent bellows-like fold. As aresult of this construction, good laminar flow is possible.

Preferably according to the invention at least two geometricallydifferent strips are wound together, one strip forming a gas-conductingtube and the other strip forming bellows folds. Alternatively it ispossible to feed multilayer flat metal strips to the production processand provide it with the bellows-like folds. The layering makes possiblea linear distribution of the bending stresses and improves acousticsound damping. In any case the metal strips can have differentthicknesses, widths, mechanical properties, and chemical makeups so thatthe different requirements can be imparted to the geometry of the tubeand bellows. Even elastomeric, glass-fiber-reinforce, or ceramic stripsor belts of laminates, compounds, or composite workpieces can beemployed. The strips, regardless of type and whether having one or morelayers, are wound in each other and fitted together such that in idealsituations a gas-tight joint is produced where they meet.

According to an embodiment of the invention the strips are initiallycontinuously roller shaped while parallel, then are deformed andpressure wound, and then the roller-shaped and wound strips are joinedtogether. Alternatively the strips are sequentially and discontinuouslyroller shaped, then wound together under pressure, and subsequently theroller-shaped and wound strips are joined together. The parallelroller-shaping allows a continuous winding process and the sequentialroller shaping is for a batch-type winding process.

The winding, preferably done with rollers on a mandrel, can take placepreferably continuously so that the finished conduit after winding andfitting together runs off a rotating mandrel. When a long mandrel iscompletely wound with the conduit, according to a batch process, fixedlengths of the conduit are pulled off the long mandrel. To connect thestrips, it is possible to deform them together, for example by foldingor crimping, or to use thermal processes, for example beam or laser-beamwelding or roller welding.

According to an embodiment of the invention the edges of the strips (2and 3) to be joined are deformed to simplify the separation and furthertreatment and for locally homogenizing the product diameter. It isparticularly advantageous when the connection ends are pressure treated.

Instead of making the folds or bellows-like turns of one piece from onefold, they can be made advantageously by joining, either deformingtogether or thermally joining, the edges of webs projecting from theedges of the trailing edge of one turn and the leading edge of anotherturn. It is also possible to form leading and trailing edges of one turnand to join the free web edges together. It is also possible to makemore than two webs and join them together.

A preferred embodiment provides that a bell-shaped inner bellows fold iswound in a valley of an outer bellows fold with diametrally extendingwebs projecting from a common bridge and connecting web. The facingbellows folds fitting almost in each other produce a very softdecouplable configuration with considerable flexibility and elasticity.Since in the same length is it is possible to fit twice as many turns orfolds, the conduit is nearly twice as flexible as it has more turns andfolds. The shapes can be produced preferably symmetrical, so that thesecond strip has as a result of the folded-over bridge or connecting weba liner function, e.g. for laminar gas flow.

Gas tightness is achieved preferably in that upper free web edges of thebell-shaped inner bellows fold are connected to adjacent web edges ofthe outer bellows fold.

It is suggested that in order to separate the conduit into standardlengths and/or to shape and join them support means are used. Theemployed support means, e.g. an ultrasound overlay, make it possiblewhen very long conduits are being produced, it is possible to make upthe desired standard length using mechanical or, preferably, thermalcutting systems.

A further advantage embodiment is that the finished conduit isconditioned for the required static and dynamic stiffness. This can bedone by subjecting, for example, the conduit to the effects of internalpressure or mechanical deformation.

A conduit made according to the invention is characterized in that it isformed with bellows folds having heights equal to a multiple of a stripthickness, preferably 25 to 75 times the thickness of the strip.

An embodiment of the invention proposes that at least two geometricallydifferent strips are wound together, one strip forming a gas-conductingtube and the other strip forming the bellows folds. The gas-conductingtube serves for laminar gas flow and the very tall bellows folds givethe conduit flexibility and elasticity.

Here preferably each bellows fold has a peak formed from the start as aclosed turn. Advantageously each bellows fold can be formed by websprojecting radially from the turns and having free edges that areconnected gas-tight together at the peak. Thus for example by doublingthe winding layer each leading edge region of one turn forms with thetrailing edge region of the preceding turn a bellows fold, so thatjoining together the outer edges of these edge regions seals the bellowsfold.

When the hooked-together interlock connections are axially slidable ineach other, the conduit has considerable axial play for extension andcompression.

According to an embodiment of the invention the valleys of the bellowsfolds are covered by strip regions of the turns. This covering can beeffected by a horizontal end region of one turn or between the hooked orinterlocked sections of a turn layer.

According to a preferred embodiment of the invention a tube-base formingstrip is formed with bell-shaped bellows folds that are each fitted in abellows fold of the other strip, free web edges of the outer bellowsfold being joined at the peak with the free edges of the inner adjacentwebs of the bell-shaped bellows fold that covers the valley of the outerbellows fold with a connecting region between its webs. The outerbellows fold containing the facing inner bell-shaped fold produces avery soft configuration of a highly elastic and flexible conduit. Thesymmetrical shape achieved in spite of the different strips hassubstantial process advantages.

Further features and particularities of the invention are seen in theclaims and the following description of embodiments of the inventionshown in the drawing. Therein:

FIG. 1 is a sectional view of several turns of a conduit or tube madefrom a strip in an embodiment of a single-layer interlocked tube withunitary radially projecting webs, compressed together on the left andstretched out in the right half of the view;

FIG. 2 is a detail of FIG. 1 in larger scale showing thecompressed-together condition of the interlocked tube;

FIG. 3 is a view like that of FIG. 1 of a different embodiment of asingle-layer interlocked tube;

FIG. 4 is a view like that of FIG. 1 of a further embodiment of asingle-layer interlocked tube;

FIG. 5 is views like those of FIGS. 1 and 2 but of a multiple-layerinterlocked tube and with the conduit or exhaust tube compressedtogether in the right half of the view;

FIG. 6 is a view like FIG. 5 with differently shaped turns or bellowsfolds;

FIG. 7 is a sectional view of several turns of a conduit or tube madefrom strip whose bellows folds have inner crests, that is formed ofclosed folds or turns;

FIG. 8 is sectional views of further embodiments of a gas-tight conduitor tube in compressed and stretched condition with captured (I) ormultilayer (II) turns;

FIG. 9 is a sectional view of several turns of a conduit or tube in acentral region with captured turns, shown in compressed condition (upperleft half of view) and stretch condition (upper right half of view andenlarged in half of view);

FIG. 10 is a sectional view of several turns of a conduit or tube in anembodiment of construction from two preshaped strips that are hookedtogether in a central region, shown in compressed condition (upper lefthalf of view) and stretch condition (upper right half of view andenlarged in lower half of view);

FIG. 11 is a view like FIG. 9 of another embodiment formed of twopreshaped strips wound into a conduit or tube;

FIG. 12 is a detail in section of further embodiments with unitary orfitted together joints of adjacent radially outwardly projecting webs ofpreformed bellows folds or turns;

FIG. 13 is a section through several turns of a conduit or tube made oftwo strips, the inner tube producing a laminar-flow tube surface and theouter tube forming the bellows folds or turns;

FIG. 14 is a view like FIG. 13 with different folds or turns;

FIG. 15 is a view like FIG. 13 with an other system for hooking togetherthe two tubes;

FIG. 16 is a view like FIG. 14 with different connections for hookingone strip to the other strip;

FIG. 17 is a view like FIG. 13 with another style of strip formingbellows folds or turns;

FIG. 18 is a view like FIG. 13 with a weld joint between the two tubes;

FIG. 19 is a view like FIG. 14 with a weld joint between the two tubes;

FIG. 20 is a view like FIG. 18 with a different weld connection;

FIG. 21 is a view like FIG. 19 with a different weld joint between thestrips;

FIG. 22 is a section through an embodiment of a conduit or tube formedof two strips, where nested-together bellows folds formed by the foldsor turns form a sort or bell; and

FIG. 23 is a schematic view of a profile-rolling system to preshape astrip with a formation projecting from its plane.

All the conduits or hoses 1 shown in section in FIGS. 1 to 22 have incommon, whether they are formed of one strip 2 (FIGS. 1 to 9) or twostrips 2 and 3 (FIGS. 10 and 11 and 13 to 22) or have one or severallayers, that the strip 2 or the strips 2 and 3 have preformedbellows-like turns or folds 4 with a height h1 or h2 of the bellowsfolds 4 formed by radially inwardly or outwardly directed webs 5 a and 5b and of a height equal to between 25 and 75 times the thickness of thestrip 2 or 3 (see FIGS. 1, 7 and 13). To preshape these webs 5 a and 5 bor the bellows folds 4, the strip 2 is passed as shown in FIG. 23between pairs of rollers 6 of a roller-shaping system 7 that has atleast one pair of rollers not in the roller plane, to which end relativeto the treatment direction 8 shown in the drawing the last roller pair 6a is somewhat lower. The strip 2 in the illustrated embodiment passesthrough another roller pair 6 b situated on an arcuate path. The thuspreshaped strip is wound together in a winding operation as an endlesshelix to form a hose.

The conduit shown in FIGS. 1 to 4 is formed of turns with singlehooked-together connections 9. With this shape the trailing end regions10 and the leading regions 11 are folded over to double-layer zones 12and 13 that in the embodiments are set outward so that the webs 5 a and5 b project radially. The upper free ends of the webs 5 a and 5 b areconnected gas-tight together, as by weld seams 14, so as to form aclosed bellows fold 4. As can be seen in the drawing, the preshaping canimpart different shapes or geometries to the webs 5 a and 5 b so that inthe stretched condition as shown in FIG. 1 they form a point or roof, inFIG. 3 are U-shaped, and according to FIG. 4 are rounded oromega-shaped, the omega shape having shown itself to be particularlydurable.

In the conduits of FIGS. 5 and 6 there are multiple interlocked layers,the individual turns being connected together at an interlock 19. Thetrailing edge region 10 and the leading edge region 11 of the strip arealso doubled at regions 12 and 13 that form outwardly bent webs 5 a and5 b. With this interlock 19 nothing can get between the joints fromoutside. The free edges of the webs 5 a and 5 b are as in theabove-described embodiments joined together after the winding operation,e.g. by roller welding, with a weld seam 14. Beam welding can be used asan alternative, as it requires no support. The shape or contour of theprojecting webs 5 a and 5 b and thus of the bellows folds 4 is selectedas for all embodiments that the necessary stiffness and static anddynamic resistance to vibration are achieved.

The conduit 1 made of a strip according to FIG. 7 has rounded bellowsfolds 4 of bellows-like turns that are preformed into closed turns, thatis the webs 5 a and 5 b are not joined at crests 15. The hooked-togetherconnection 9, which is produced by pressing or that can be weldedtogether against an internal mandrel, causes the edge region 17 of eachturn to extend over and cover the open bottom 16 of the adjacent bellowsfold 4 for laminar gas flow.

FIGS. 8, 9, and 12 show further possible variants of the interlocks 9and 19 of the individual turn layers in conduits 1 formed as describedabove of a strip 2 with radially projecting webs 5 a and 5 b joined byshaping or thermally joined together to form bellows folds 4. Accordingto FIG. 8, the single hooked-together connection is shown at I, themultiple hooked-together connection at II, and a central hooked-togetherregion in FIG. 9. FIG. 12 shows embodiments of the connection of thefree ends of radially extending webs 5 a and 5 b, to the left joined bywelding and in the center and to the right by crimping together.

Unlike the above-described embodiments the conduits 1 of FIGS. 10 and 11are each formed by two strips 2 and 3 that are wound together. Both theinner and the outer strips have outwardly projecting webs 5 a and 5 b,the webs 5 b of the inner strip 3 being connected with the adjacent webs5 a of the outer strip 2 to form gas-tight bellows folds 4. A variationis shown in FIG. 10 where in each turn of the outer strip 2 spaced webs5 a and 5 b are paired with one web 5 a of the inner strip 3, and thefree edges of all these webs are connected together (by welding) atpeaks 15. The individual turns are connected together at a hookconnection 9 in the centers. Generally horizontal edge regions 18 of theinner strip 3 impart to the conduit 1 the desired shape for laminar gasflow. This is also achieved in the conduit 1 of FIG. 11 in that thestrip section 20 between the folded webs 5 b forms the desired hoseshape.

Further conduits 1 formed of two strips 2 and 3 are shown in FIGS. 13 to21 where the inner strip 3 provides the tube geometry for laminar gasflow and the outer strip 2 has the bellows folds in which the webs 5 aand 5 b form seamless, that is closed, peaks. The figures show thedifferent possible shapes for the bellows folds 4. Furthermore the lowerhalves of the figures separately show the outer strip 2 and the innerstrip 3 and the various ways of connecting the turns according to thepreshaping of the strips 2 and 3. FIGS. 18 to 21 show that instead offitting together and thereby coupling the individual layers it ispossible to join them thermally by a weld seam 14.

A particular embodiment of a conduit 1 formed of two preshaped strips 2and 3 is shown in FIG. 22. The radially symmetrically projecting webs 5a of the outer strip 2 are connected to the webs 5 b at their outer freeedges with the free edges of the inner strip 3 forming the hose base,with the folded-over connecting web 21 covering the valley 16 of thebellows fold 4 formed by the webs 5 a. The outer bellows fold 4 closesan inner bellows fold 22 formed by the strip 3 and opening toward it, sothat the combination of the outer bellows fold 4 and the inner bellowsfold 22 forms a bell-like shape. In this embodiment the free edges ofthe webs 5 a and 5 b are joined together by folding; similarly the foldapices 15 could be joined or connected thermally. The bell shape of thebellows-like turns 4 and 22 forms the same overall dimension as adouble-turn arrangement and thus imparts considerable flexibility andelasticity to the conduit 1.

In every case the conduit 1 is produced in a single production step byspiral winding. The rolling method to make the very tall webs or bellowsfolds or bellows-like turns, the deforming method, the mechanical orthermal jointing by means of which the webs are joined togethergas-tight can take place in a continuous process or in a batch process.The resultant conduit is not only perfectly gas tight, but as a resultof the deep bellows folds or turns is extremely flexible and elastic andprofiles and gives good laminar gas flow regardless whether the conduitis formed from one strip or two or more strips in one or more layers.

1-24. (canceled)
 25. A method of making a conduit (1) forvibration-stressed piping systems, in particular as a motor-vehicleexhaust pipe, from a preshaped strip (2 or 3), in particular a metalstrip, that is helically wound with bellows-like turns (4 or 22), thewound-together layers formed by a strip width having singlyhooked-together or multilayer interlocked edges (9; 19) joined byinterfitting, welding, or a similar joining process, the strip (2 or 3)being preshaped by at least one roller pair outside the plane and beingthereby deflected into an arcuate path with in both stretched andcompacted condition fold height (h1 and h2) of the folds (4 and 22)equal to a multiple of the strip thickness, characterized in that thefolds (4 and 22) are made by connecting the edges of webs (5 a and 5 b)projecting radially from the trailing edge (10) of one turn and theleading edge (11) of another turn.
 26. The method according to claim 25,characterized in that the web edges are deformed and joined together atpeaks (15).
 27. The method according to claim 25, characterized in thatthe web edges are thermally joined together at peaks (15).
 28. Themethod according to claim 25, characterized in that a bell-shaped innerfold (22) is wound in a valley of an outer fold (4) with diametrallyextending webs (5 b) projecting from a common bridge and connecting web(21).
 29. The method according to claim 28, characterized in that upperfree web edges of the bell-shaped inner fold (22) are connected toadjacent web edges of the outer fold (4).
 30. A conduit (1) forvibration-stressed piping systems, in particular as a motor-vehicleexhaust pipe, made from a preshaped strip (2 or 3), in particular ametal strip, that is helically wound with bellows-like turns (4 or 22),the wound-together layers formed by a strip width having singlyhooked-together or multilayer interlocked edges (9; 19) joined byinterfitting, welding, or a similar joining process, the folds (4 and22) having heights (h1 and h2) equal to a multiple of a strip thickness,produced by the method of claims 1 to 5, characterized in that each fold(4) is formed by webs (5 a and 5 b) projecting radially from the turnsand having free edges that are connected gas-tight together at the peak(15).
 31. The conduit according to claim 30, characterized in that atube-base forming strip (3) is formed with bell-shaped folds (22) thatare each fitted in a fold of the other strip (2), free web edges of theouter fold (4) being joined at the peak (15) with the free edges of theinner adjacent webs (5 b) of the bell-shaped fold (22) that covers thevalley (16) of the outer fold (4) with a connecting region (21) betweenits webs (5 b).
 32. A conduit (1) for vibration-stressed piping systems,in particular as a motor-vehicle exhaust pipe, made from a preshapedstrip (2 or 3), in particular a metal strip, that is helically woundwith bellows-like turns (4 or 22), the wound-together layers formed by astrip width having singly hooked-together or multilayer interlockededges (9; 19) joined by interfitting, welding, or a similar joiningprocess, the folds (4 and 22) having heights (h1 and h2) equal to amultiple of a strip thickness, produced by the method of claims 1 to 5,characterized in that each fold (4) is formed from a turn layer with apeak (15) of a preshaped closed turn and has a gas-tight interlockconnection (9 or 19).